Dude ACE matched if not upstaged the first Xenoblade and it has one of the best OST's ever in an RPG. It's a super group of gamings best composers. The first game had among many others the composer who did Guiles them in SFII. Composers from Final Fantasy, Smash Bros, and others. Mitsuda leads the group who is a legend himself. They also hired a group of Celtic singers for some tracks, It's flat-out gorgeous.
Well let's not belittle Skyrim's OST. Mitsuda is a legend and ACE is fantastic but Soule is very highly renowned in his own right. Skyrim has truly fantastic music, as does Oblivion and Morrowind. It's just a very different approach and style.
Xenoblade Chronicles 1 and 2 OSTs are masterful though.